In an electronic switching system (ESS), a signaling refers to a transmission of switching information between a subscriber and an exchange or between two exchanges.
A signaling for exchanging information between a subscriber and an exchange is called a subscriber line signaling, wherein the information includes, e.g., a call request signal, a call release signal, address signals, a ringing signal, a metering pulse and tones and recorded announcements.
A signaling for exchanging information between two exchanges is called an interexchange signaling. The interexchange signaling includes a line signal and a register signal. The line signal represents the state of an interexchange trunk line, e.g., a seizure signal, a release signal, called party on/off supervisory signals and relates to the state of a called line. The register signal is a signal interchanged between two registers or two similar control equipments. The register signal generally includes a proceed-to-send signal, an address signal and signals indicating the result of a call attempt.
There are a plurality of types of the interexchange signalings. Especially, in an R1 signaling, the line signal uses a frequency of 2600 Hz in transmission lines. The register signal is made of two frequencies out of six frequencies and may be transmitted on a link-by-link basis, wherein the six frequencies used in the R1 register signals are 700, 900, 1100, 1300, 1500 and 1700 Hz.
In an R2 signaling, the line signal uses a frequency of 3825 Hz in transmission lines. The register signal uses two frequencies out of six frequencies and may be transmitted on an end-to-end basis, wherein the six frequencies used in the R2 register signals are 1380, 1500, 1620, 1740, 1860 and 1980 Hz for forward signaling and 1140, 1020, 900, 780, 660 and 540 Hz for backward signaling.
As described above, each of interexchange signaling types has a different format from one another and different interexchange signaling type is used in different region or nation.
Since, however, the ESS can interchange the information with another ESS only if the interexchange signalings in two ESS's are identical, e.g., an ESS adapting the R1 signaling can interface only with an ESS adapting the R1 signaling and an ESS adapting R2 signaling can interface only with an ESS adapting R2 signaling, the ESS lacks flexibility in the interexchange signaling between exchanges.